An internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. Intake and exhaust valves are operated by a camshaft. The air flows into the combustion chamber while the intake valve is open, and air is exhausted from the combustion chamber while the exhaust valve is open.
Optimal operations of the intake valve or the exhaust valve are determined according to a rotational speed of the engine. That is, lift and open/close timing of the valves are controlled according to the rotational speed of the engine. A variable valve lift (VVL) apparatus has been developed in which the valves are operated for various valve lifts according to the rotational speed of the engine for realizing optimal operations of the valves. For example, the VVL has a plurality of cams fastened to a camshaft and operating the valves with different valve lifts. The cams for operating the valves are selected according to a vehicle condition.
When the plurality of cams are provided to the camshaft, the operation of the intake valve or the exhaust valve by selectively changing the cams is complex, and interference between engine parts may occur.
Further, when the plurality of cams are independently operated to prevent the interference between the engine parts, an additional element is required for operating each cam, thus increasing cost.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.